The present invention relates to a semiconductor element and a semiconductor device. In particular, the present invention relates to a semiconductor element having a specific configuration and a semiconductor device including the semiconductor element.
In a conventional semiconductor device including a conventional semiconductor element, there is a time when it is necessary to increase an allowable limit of an electrical current (an allowable electrical current) to be flown in the semiconductor element. As an example of such a conventional semiconductor device includes an electro-static discharge (ESD) protection circuit that protect an electrical circuitry from an electro-static discharge (ESD). In general, the ESD protection circuit is formed of a diode. The ESD circuit may be designed to increase the allowable electrical current to be flow through the diode (a p-n connection), so that it is possible to discharge a surge electrical current with a high peak value outside the conventional semiconductor device.
FIG. 5 is a circuit diagram showing a configuration of an ESD protection circuit 120 disposed in a semiconductor integrated circuit 100 as the conventional semiconductor device.
As shown in FIG. 5, the ESD protection circuit 120 is composed of static electricity protection elements ESD1 and ESD2 using diodes. More specifically, the static electricity protection element ESD1 is connected between an input terminal PAD and a positive power source VDD, and the static electricity protection element ESD2 is connected between the input terminal PAS and ground (GND), respectively. Further, the input terminal PAD is connected to an inner circuit 112 of the semiconductor integrated circuit 100. More specifically, the input terminal PAD is connected to a transistor MN of the inner circuit 112 as shown in FIG. 5. It should be noted that, in addition to the input terminal PAD, the ESD protection circuit 120 may disposed at a location necessary for the static electricity protection such as an output terminal, a power source wiring, and the like.
Patent Reference has disclosed a static electricity protection element composed of a diode having a rectangular shape, and a size of the diode is determined based on the allowable static electricity (the allowable ESD). For example, when it is necessary to achieve the allowable ESD of 2,000 V according to a human body model method (HBM method), the diode needs to have a size that is not damaged when an electrical current of 1.33 A flows through the diode according to the TDR-TLP measurement method.
In the HBM method, the allowable static electricity is measured in a discharge model that a human body contacts with a semiconductor. Further, in the TDR-TLP measurement method, a rectangular wave is applied to a measurement subject. Then, an oscilloscope is used to observe and analyze a reflection wave from the measurement subject, so that an operational characteristic of the measurement subject upon applying the ESD.
Patent Reference: Japanese Patent Publication No. 08-181334
In general, it has been known that the allowable electrical current passing through the diode is proportional to a length of a p-type region facing an n-type region in the diode (that is, a length of a portion of the diode functioning as the p-n connection, also referred to as a circumferential length in the following description). For example, it is assumed that, when the diode has the circumferential length of 10 μm, the diode has the allowable electrical current of 0.1 A. In order for the diode to have the allowable electrical current of 1.33 A, it is necessary for the diode to have the circumferential length of 133 μm (=10 μm×(1.33 A/0.1 A)).
More specifically, with the diode disclosed in Patent Reference as an example, the circumferential length will be explained in more detail. According to Patent Reference, the static electricity protection element is composed of a diode 200, that is, a Zener diode, as the static electricity protection element.
FIGS. 6(a) and 6(b) are schematic views showing a configuration of the diode 200 as the static electricity protection element. More specifically, FIG. 6(a) is a schematic plan view showing the diode 200, and FIG. 6(b) is a schematic sectional view showing the diode 200 taken along a line C-C′ in FIG. 6(a).
As shown in FIGS. 6(a) and 6(b), the diode 200 includes a P-type substrate 201; an N-type well 202 formed in the P-type substrate; and a P-type high concentration diffusion layer 203 and an N-type high concentration diffusion layer 204 formed in the N-type well 202. Further, the P-type high concentration diffusion layer 203 is separated from the N-type high concentration diffusion layer 204 with an element separation oxide film 205 in between. The P-type high concentration diffusion layer 203 is formed in a rectangular shape, and the N-type high concentration diffusion layer 204 is formed in a ring shape surrounding a circumference of the P-type high concentration diffusion layer 203 formed in a rectangular shape.
In the static electricity protection element disclosed in Patent Reference, as one of methods of defining the circumferential length, the circumferential length of the diode 200 may be defined as a length of an outer circumference of the P-type high concentration diffusion layer 203 formed in a rectangular shape (represented with a hidden line in FIG. 6(a)). According to this definition, in order for the diode 200 to have the allowable electrical current of 1.33 A, it is necessary for the P-type high concentration diffusion layer 203 to have the circumferential length of 133 μm.
As described above, the allowable electrical current of the diode is determined by the circumferential length. Further, in order to reduce the size of the semiconductor device, it is necessary to reduce the size of the diode as much as possible. Accordingly, when it is necessary to increase the allowable electrical current of the diode, especially the diode as the static electricity protection element, it is necessary to increase the circumferential length thereof as much as possible while restricting the size of the diode as a whole.
As described above, the static electricity protection element disclosed in Patent Reference, the P-type high concentration diffusion layer 203 is formed in a rectangular shape (or an island shape), and the N-type high concentration diffusion layer 204 is formed in a ring shape surrounding the circumference of the P-type high concentration diffusion layer 203 formed in a rectangular shape. Accordingly, it is difficult to reduce the circumferential length of the N-type high concentration diffusion layer 204. As a result, it is difficult to reduce the side of the diode 200, thereby increasing the side of the ESD protection circuit.
In view of the problems of the conventional semiconductor element described above, a subject of the present invention is to provide a semiconductor element and a semiconductor device capable of reducing a size thereof while maintaining the allowable electrical current at a high level.
Further objects and advantages of the invention will be apparent from the following description of the invention.